In the past various techniques have been used to apply magnetically attractable toner particles to a latent magnetic image. Generally this has been achieved by cascading the magnetically attractable toner particles over the latent magnetic image such as in the manner disclosed in U.S. Pat. No. 3,698,005. An alternate technique is disclosed in U.S. Pat. No. 3,640,247 wherein a non-magnetizable tube containing a rotatable row of bar magnets is used to deliver toner particles from a sump to a shelf adjacent a drum having a latent magnetic image in the surface thereof.
The present invention relates to an apparatus and method for applying magnetically attractable toner particles to a latent magnetic image in such a way that a very wide range of imaging surface velocities can be achieved with excellent uniformity and image density across the width of latent magnetic images much wider than hitherto achieved.